This invention relates to novel crosslinkable compositions comprised of hydroxy terminated polydiene polymers, polyisocyanates, and reinforcing agents. More specifically, the invention relates to the use of particular dihydroxy terminated hydrogenated diene polymers in crosslinking with polyisocyanates to produce products which are useful in coating compositions and in adhesive and sealant compositions.
Hydroxy functional polydiene polymers (polydiene diols) are well known. U.S. Pat. No. 5,393,843 discloses that formulations containing these polymers, a melamine resin, and an acid catalyst can be cured by baking under normal bake conditions. This same patent also discloses that these polymers can be mixed with isocyanates to yield compositions which cure at ambient temperature. It is known that, for instance, hydrogenated polybutadiene diols (EB diol) can be crosslinked by reaction with polyisocyanates at stoichiometry near 1/1 NCO/OH (NCO represents the isocyanate functionality which is active in the crosslinking reaction and OH represents the hydroxyl functionality). However, for economic reasons, it is only practical to make hydrogenated polydiene diols of relatively high hydroxyl equivalent weight (OH ew). However, these compositions based on hydroxy functional polydiene polymers cured with a crosslinking agent are usually fairly soft because the polymers are relatively high in hydroxyl equivalent weight, i.e., above about 750 ew OH (hydroxyl equivalent weight is the number average molecular weight divided by the number of functional groups per molecule) and thus are elastomeric and rubbery in nature and, although they can be very useful in some applications, they are too soft and too low in cohesive strength to be widely useful in applications such as hard coatings.
Attempts to increase hardness and adhesion by increasing crosslink density by simply mixing the polydiene diols and the polyisocyanate with a reinforcing agent, such as a low molecular weight diol or triol, were unsuccessful because the reinforcers are relatively polar and so are incompatible with the relatively nonpolar polydiene polymers, Incompatibility of the components leads to poor properties, such as gloss, in the cured composition or, even worse, the compositions may phase separate upon storage prior to cure.
I have discovered that this incompatibility problem can be overcome by synthesizing polyurethane resins based on a polydiene diol, a reinforcing diol or triol, and a polyisocyanate at appropriate NCO/OH ratios which are not close to 1:1. Essentially, this involves carrying out a limited reaction among the three components in order to render them compatible.
This invention provides a process for producing a polyurethane resin from a hydrogenated polydiene diol or polyol having a hydroxyl equivalent weight of 750 to 10000, a reinforcing agent, preferably a diol or triol, having a functional group, preferably hydroxyl, equivalent weight of 30 to 200, and a polyisocyanate. In a first preferred embodiment, the process comprises reacting at least one of the polydiene diol (or polyol) or the reinforcing agent with the polyisocyanate at a NCO/functional group molar ratio (NCO refers to the isocyanate functionality on the polyisocyanate and functional group refers to the functionality on the polydiene diol or polyol and the reinforcing agent) of 0.4 to 0.7 to form a stable reaction product, adding to this reaction product an additional sufficient amount of the polyisocyanate and, as needed, one or both of the polydiene diol (or polyol) or the reinforcing agent to bring the NCO/functional group ratio up to 0.9 to 1.1 and to achieve a polydiene diol (or polyol) content of 35 to 80%w (on solids basis) (%w means percent by weight) and a reinforcing agent content of 2 to 17%w (on solids basis), and reacting this final mixture to form a crosslinked polyurethane product. This invention also provides a novel polyurethane resin which is the reaction product of the first step of the process.
In a second preferred embodiment, the process comprises reacting at least one of the polydiene diol (or polyol) or the reinforcing agent with the polyisocyanate at a functional group/NCO ratio of from 0.25 to 0.55 to form a stable isocyanate terminated reaction product, adding to this stable reaction product an additional sufficient amount of one or both of the polydiene diol (or polyol) or the reinforcing agent and, as needed, the polyisocyanate to bring the functional group/NCO ratio up to 0.9 to 1.1 and to achieve a polydiene diol (or polyol) content of 35 to 80%w (on solids basis) and a reinforcing agent content of 2 to 17%w (on solids basis), and reacting this final mixture to form a crosslinked polyurethane product. This invention also provides a novel polyurethane resin which is the reaction product of the first step of this process.
In a third preferred embodiment, the process comprises mixing the polydiene diol (or polyol), the reinforcing agent, and a blocked polyisocyanate curing agent together such that the molar ratio of functional group to completely deblocked NCO would be from 0.9 to 1.1, the polydiene diol or polyol content is 35 to 80%w (on solids basis) and the reinforcing agent content is 2 to 17% w, then reacting these components at a temperature, usually about 80xc2x0 C. to about 150xc2x0 C., and for a time, usually about 0.5 hour to about 5 hours, sufficient to deblock enough of the polyisocyanate such that a stable partially reacted polyurethane resin is formed, and finally, deblocking the remainder of the blocked polyisocyanate and reacting it with the partially reacted polyurethane resin to form a crosslinked polyurethane product. This invention also provides a novel polyurethane resin which is the reaction product of the polydiene diol or polyol, the reinforcing agent, and the deblocked portion of the blocked polyisocyanate in the second step of the process. Hydroxy functional polydienes are preferred for use herein as are reinforcing agents which are diols or triols.